Cathodic device for electrolytic cells having a moving mercury cathode



Aug. 26, 1958 C DEPREZ ETAL .CATHODIC DEVICE FOR ELECTROLYTIC CELLS HAVING A MOVING MERCURY CATHODE Filed Jan. 4, 1955 Patented Aug. 26, 195% ice CATHODIC DEVHIE FOR ELECTROLYTIC CELLS HAVING A MQViNG MERCURY CATHUDE Charles Deprez and Jean Clement, Brusseis, Beigiuin, assignors to Solvay & ie., Brussels, Prelgium, a lieh gian company Application January 4, 1%5, Serial No. 47?,746

Claims priority, application Beigium ianuary 27, 1954 13 Claims. (Cl. 204-219) The invention relates to a cathodic device for electrolytic cells having a moving mercury cathode and more particularly to the metallic surface forming the support for the mercury in cells of the vertical type for the electrolysis of salt solutions whose cations, discharged at the cathode, are capable of forming amalgams with iii Up to now, no satisfactory solution has been found to overcome this difliculty.

One known proposal relates to the use of a system of steps provided in the supporting body, along which the mercury flows in the form of successive cascades.

A second known proposal seeks to counteract the tendency for the liquid metal sheet to separate, by causing it to flow on a support provided with vertical grooves, the individual grooves being very closely spaced.

A third known proposal for overcoming the above mentioned ditficulty relates to the use of a smooth vertical support whose vertical edges approach each other towards its lower portion.

Application of either of the first or second proposals leads to a reduction in the occurrence of secondary reactions without eliminating them completely.

Application of the third proposal requires a very considerable mercury feed. Moreover in this latter case the speed with which the mercury sheet falls is considerable and provokes a strong whirling in the electrolyte. the particular case of the electrolysis of aqueous solutions of alkali metal chlorides, this phenomenon is accompanied by an appreciable loss in yield due to the recombination of the chlorine dissolved in the electrolyte with the amalgamated alkali metal. the high mercury feed the alkali metal concentration is normally low and in order to obtain concentrations suitable in practice, it is necessary to provide supports of great length, so that such electrolytic cells would have to be of excessive height.

It is an object of the present invention to overcome the disadvantages inherent in the known proposals by means of a device which allows a considerable slowing down of the mercury flow whilst maintaining the metal spread on the supporting surface and by covering the latter completely with a thin sheet.

According to one aspect the invention is characterised in that the metal support of the mercury is provided with two sets of grooves, inclined in opposite directions and intersecting in such a manner that their intersection determines angles the bisectors of which extend horizontally.

On account of i The principle of the cathodic device according to the invention is, by way of example, diagrammatically illustrated in Figures 1 and 2 of the accompanying drawings.

Figure 1 shows a front view of a mercury supporting plate provided with a means for the mercury feed,

Figure 2 is a vertical section of this support,

Figure 3 is a perspective of a cathode.

Referring to the drawings the support 1 is provided with grooves 2 and 3 which are, according to this particular example, perpendicular to one another. On the support 1 is fixed a tank 4, said tank being provided with an overflow 7 known per se, which tank receives a supply of mercury 5 through a pipe 6.

The mercury coming from overflow 7 flows along the support 1 in a very thin layer of about one-tenth of a millimetre. its vertical fall is checked by the grooves 2, 3 which have a depth of about 0.3 mm. and a width of about 1.5 mm. The channels or grooves, inclined in opposite directions and forming a grid of about 4 mm. squares, direct part of the mercury towards the external edges of the support and thus contribute to maintain a perfect continuity of the mercury sheet on the gofered support.

By way of example, a supporting plate grooved as described above has been fed with mercury at a flow of l litre/minute per metre of width of the support. The cathode thus formed, working in an electrolytic cell at a cathode current density of 30 amp/sq. dm., has produced an amalgam whose alkali metal concentration was 0.5 percent by weight, the useful height of the cathode being about 2 metres.

The effect of checking of the fall of and spreading of the mercury caused by the grooves is dependent mainly on the viscosity and the surface tension of the amalgam which flows on the metallic support. These factors continue to increase continually along the flow of mercury. In order to take into account these variations, according to another aspect of the invention the grooves of one set may be no longer parallel to one another. The angles which they form with the horizontal become greater and greater the closer they approach the lower part of the support. However, an angle of 45 seems to be the maximal limit.

The supporting surfaces can be plane or curved as desired. In the case of a vertical cell the support can be of tubular form and each of the two sets of grooves constitute one or more helices in the manner of a multiple thread screw, the said helices can be of uniform pitch or, in the case when it is desired to take into account the variation of the viscosity and/or of the surface tension of the amalgam, the pitch can be variable and increase towards the lower part of the support.

The supporting surfaces can be formed of plates having grooves on one or two faces, which plates can be provided internally with an arrangement for the circulation of a heating or cooling fluid, in order to regulate the temperature of the cathode.

Figure 3 of the accompanying drawings illustrates by way of example a cathode constituted by a flat hollow body of iron grooved on both faces. The said cathode comprises two opposite surfaces 8, provided with grooves, and whose horizontal upper edges 9 form overflows 1E3 fed with mercury from two cavities 11 separated by a partition 12. The mercury is fed into the cavities through tubes 13, overflows at 10, flows along the grooved surfaces 8, and the amalgam produced during the electrolysis enters a collector 14 from where it leaves the electrolytic cell through a tube 15. The cathode is connected with the source of electric current by current supply means to. Circulation of the heating or refrigerating fluid takes place through tubes 17 and iii.

The metallic surfaces which are not covered by mercuiy should not be brought into .contact with the electrolyte; for this reason they are covered by a protective insulating coating. As an insulation there can be used an adhering Coating applied to the partition 12, the current supply means 16, the mercury feeding tubes 13, and the collector 14. For constructional reasons, the lateral faces 19 of the cathode assembly may be covered by an insulating elastic sheet 20 forming a joint and secured to the body by terminal plates 21 of metal protected by an insulating layer, the plates being kept in position by nuts 22 and washers 24 screwed on rods 23. In the same way, tubes 17 and 18 passing through the joint 20 and plates 21 are provided with screw nuts 25 and washers 26. After the assembly, the non-protected metal ends which protrude from the plates 21 are likewise covered with an insulating coating.

We claim:

1. In an electrolytic cell including a moving mercury cathode, a support surface for the mercury, said support surface comprising a monoplanar surface area for receiving the mercury cathode stream interrupted by two sets of grooves extending inwardly in a direction away from the exposed surface of said mercury cathode stream, said two sets ofgrooves being inclined in opposite directions and intersecting in such a manner. that their intersections define angles the bisectors of which extend horizontally.

2. In an electrolytic cell including a moving mercury cathode, a support surface for the mercury, said support surface comprising a monoplanar surface area for receiving the mercury cathode stream interrupted by two sets of intersecting grooves extending inwardly in a direction away from the exposed surface of said mercury cathode stream, corresponding grooves in the two sets being inclined at substantially equalbut opposite angles to the horizontal.

3. In an electrolytic cell including a moving mercury cathode, a support surface for the mercury, said surface being composed of an electrically conductive material and comprising a monoplanar surface area for receiving the mercury cathode stream interrupted by two sets of intersecting grooves extending inwardly in a direction away from the exposedsurfaceof said mercury cathode stream, corresponding grooves in the twosets being inclined at substantially equal but opposite angles to the horizontal.

4. An electrolytic cell as defined in claim 3 in which said monoplanar area is defined by a flat surface of the support.

5. An electrolytic cell as defined in claim 3 in which said monoplanar area is defined by a curved surface of said support.

6. In an electrolytic cell of the vertical type including a moving mercury cathode, a vertical support surface for the mercury, said surface being composed of an electrically conductive material and comprising a monoplanar surface area for receiving the mercury cathode stream interrupted by two sets of intersecting grooves extending inwardly in a direction away from the exposed surface of said mercury cathode stream, corresponding grooves in the two sets being inclined at substantially equal but opposite angles to the horizontal.

7. An electrolytic cell as defined in claim 6 in which the support includes a cylindrical portion on which said grooves are provided.

8. An electrolytic cell as defined in claim 7 in which the axis of the cylindrical portion extends in a direction perpendicular to that of the cell.

9. In an electrolytic cell of the vertical type including a moving mercury cathode, a vertical support surface for the mercury, said surface comprising a monoplanar surface area for receiving the mercury cathode stream interrupted by two sets of intersecting grooves extending inwardly in a direction away from the exposed surface of said mercury cathode stream, corresponding grooves in the two sets being inclined at substantially equal but opposite angles to the horizontal, the grooves of each of the respective sets forming increasing angles with the horizontal towards the lower portion of said surface.

10. A support surface for a mercury stream for use an electrolytic cell of the vertical type including a moving mercury cathode, said surface being the surface of a body provided with means for controlling the temperature of said cathodeand being composed of an electrically conductive-material and comprising a monoplanar surface area for receiving the mercury'cathodestream interrupted by two sets of intersecting grooves extending inwardly in a direction away from the exposed surface of said mercury cathode stream, corresponding grooves in the two sets being inclined at substantially equal but opposite adjusted.

12. A vertical support surface for a mercury stream for use in an electrolytic cell of the vertical type including a moving mercury cathode, said surface being-the surface of a body provided with means for-controlling'its temperature, said surface comprisingga-rnonoplanar surface area for receiving the mercury cathode stream interrupted by two sets of intersecting grooves extending-inwardly in a direction away from the exposed surface of said mercury cathode stream, corresponding grooves in the two sets being inclined at substantially equal but opposite angles to the horizontal, the grooves of each of-the respective sets forming increasing angles with the horizontal towards the lower portion of said surface.

13. A support surface as defined ,in claim 12 provided with means for circulating a fluid withinthe body having said support surface as its outer surface, whereby the temperature of the moving mercury cathode may be adjusted.

References Cited in the file of this patent UNITED STATES PATENTS 733,643 Gurwitsch July 14, 1903 1,176,551 Heinemann Mar. 21, 1916 FOREIGN PATENTS 692,954 Germany June 29, 1940 

1. IN AN ELECTROLYTIC CELL INCLUDING A MOVING MERCURY CATINODE, A SUPPORT SURFACE FOR THE MERCURY, SAID SUPPORT SURFACE COMPRISING A MONOPLANAR SURFACE AREA FOR RECEIVING THE MERCURY CATHODE STREAM INTERRUPTED BY TWO SETS OF GROOVES EXTENDING INWARDLY IN A DIRECTION AWAY FROM THE EXPOSED SURFACE OF SAID MURCURY CATHODE STREAM, SAID TWO SETS OF GROOVES BEING INCLINED IN OPPOSITE DIRECTIONS AND INTERSECTING IN SUCH A MANNER THAT THEIR INTER- 